The Study Of Hexagonal Assembly Pin Power Reconstruction For Fast Reactor

The development of fast reactor is important for solving the world’s energy problems and it is necessary to make sure the reactor meets safety requirements both at operation and the beginning of design.The power distribution of reactor is state parameter directly related to reactor safety,so it should be monitored with accuracy.As a numerical method for the reactor diffusion calculation,the nodal expansion methods(NEM)has been developed and widely used because of its advantages of high calculation speed and precision.However,this method could only provide the average information of the node and can’t calculate the pin power of the reactor.Therefore,pin power reconstruction algorithm should be supplemented for it.In this paper,the modulation method based on node expansion method has been selected to calculate the pin power of the hexagonal assembly of the fast reactor.In this paper,the hexagonal node flux distribution is interpolated by the high oder polynomial,the numerical methods of corner flux and polynomial expansion coefficient have been showed and the detailed theoretical derivation is presented.The developed pin power reconstruction program for hexagonal assembly named HexReac and it has been coupled to the program which uses the nodal expansion method.This work is necessary for the validation.In practical application,Serpent is used to homogenize the assembly,and the pin power reconstruction of heterogeneous assembly is realized.As part of validation,the homogeneous node and heterogeneous node questions are studied respectively by numerical test.The reference pin power of homogeneous assembly,which includes the results of two different sizes of mesh: 96 triangles/assembly and384 triangles/assembly,are calculated by finite difference program named CITATION.The reference pin power of heterogeneous assembly is calculated by the Monte Carlo program named Serpent which has done the whole core transport calculation.We can get the following conclusion from the two types of numerical verification: compare the result of homogeneous assembly calculated by CITATION with HexReac,when the assembly is divided into 96 triangles,the maximum relative erro of the power distribution of fuel nodes is 3.56%、the relative erro of the maximum power of the fine mesh is 0.39%;When the assembly is divided into 384 triangles,the maximum relative erro of the power distribution of fuel nodes is 4.86%、the relative erro of the maximum power of the fine mesh is 0.40%;Change the insertion depth of the control rod and the relative errors of the power distribution calculated by HexReac have a little change,which did not affect its calculation accuracy.HexReac program have a high precision when it calculates the power distribution of homogeneous assembly,which can reach the same level as CITATION.Compare the results of heterogeneous assembly calculated by Serpent with HexReac,the maximum relative erro of the power distribution of fuel pins is 2.54%,the relative erro of the maximum pin power is 0.39%,and the deviation is very small.The HexReac program have a high computational accuracy,it can meet engineering requirements and be used for engineering project’s pin power reconstruction calculation.